During the manufacture of many parts such as plastic molded closure caps, a number of defects in the closure cap may exist which should cause the cap to be rejected. Commonly, closure caps of this type have a liner inserted therein against the inner surface of an end wall of the cap. Typically, the cap has a skirt projecting annularly from the peripheral rim of the end wall and the skirt may include a closure or sealing mechanism such as threads for cooperation with mating threads around the neck of a bottle, container, or the like. Examples of defects in such closure caps include a liner which is positioned off-center within the closure, a missing liner, a malformed liner (commonly referred to as a “moon-cut liner”), a cap which is asymmetric or off-round, a cap having an edge broken or flashing on the edge from extraneous plastic material, a pull tab defect on the liner caps with excessively large “gates” resulting from the molding process, or other similar problems. Such flaws or defects are sometimes produced during the manufacturing process, or as a result of contamination or damages after manufacture but prior to the filling of the container.
Machine vision systems represent one technology for acquiring or sensing an image of at least a selected portion of a work piece, such as a cap as previously described, through an electronic sensor or camera. The image generated by the camera is then analyzed by a computer program for one or more of the above-described defects. Vision systems are commonly used to determine the existence of any marks or defects in the image of the cap and the acceptability of any such marks or defects by use of a vision computer as described.
While human vision may outperform its automatic equivalent in the ability to analyze very complex, everyday scenes, when it comes to repeated tasks, such as the inspection of plastic molded caps over and over again, a human observer understandably tires, loses concentration, and makes mistakes. Machine vision inspection of such articles is known to provide some important advantages, including sophisticated image processing/analysis, repeatable performance, image acquisition for diagnosis and set up, ability to inspect a variety of articles in large tolerance and required part placement. Moreover, at inspection rates of up to 1600 parts per minute or more, each part or cap spends on the order of 33 milliseconds at an inspection station. At such speeds, only a machine vision system is fast enough to reliably and repeatedly inspect such articles.
While known vision systems have the above described advantages for inspecting articles such as plastic molded caps and the like, they do have specific and significant limitations. Vision systems typically rely on video cameras to image the article to be inspected and detect any flaws. The resolution of the camera, or its ability to detect a flaw, is directly related to its ability to capture an accurate and reliable image of each individual cap, article, or similar item. Typically, plastic molded caps are manufactured by the hundreds of thousands and each individual cap must be inspected by the vision system for quality control purposes. The caps are typically gathered in an accumulated mass and are, at best, similarly oriented on a flat surface. For accurate vision inspection and detection of flaws, the vision system must be able to precisely and accurately produce an image of each individual cap without interference from the surrounding environment or other caps. Furthermore, inspection rates required of such systems mandate that the individual images be serially produced, analyzed, and acted upon accordingly for each individual cap, once again without interference, for accurate detection of relatively small flaws or problems.
One problem in efficiently creating photographic records of each plastic molded cap is providing enough separation between adjacent caps on a conveyor leading to the vision system. One solution is disclosed in U.S. Pat. No. 6,384,421, assigned to the assignee of this invention and hereby incorporated by reference entirely. Vision systems of this type separate caps by funneling a mass of caps into a single-file conveyor belt and then providing a vertical incline or ramp to accelerate and separate each cap from adjacent caps. This process is effective, but often requires a relatively large space and floor space in most industrial settings is limited. Therefore, an improved vision system that allows high-precision and high-speed inspection while occupying a small foot-print is needed.